[BOLT] Strip redundant AdSize override prefix

Since LLVM MC now preserves redundant AdSize override prefix (0x67), remove it
in BOLT explicitly (-x86-strip-redundant-adsize, on by default).

Test Plan:
`bin/llvm-lit -a bolt/test/X86/addr32.s`

Reviewed By: rafauler

Differential Revision: https://reviews.llvm.org/D120975

bolt/include/bolt/Core/MCPlusBuilder.h

@@ -1282,7 +1282,8 @@ public:
 
   /// Replace instruction with a shorter version that could be relaxed later
   /// if needed.
-  virtual bool shortenInstruction(MCInst &Inst) const {
+  virtual bool shortenInstruction(MCInst &Inst,
+                                  const MCSubtargetInfo &STI) const {
     llvm_unreachable("not implemented");
     return false;
   }

bolt/lib/Passes/BinaryPasses.cpp

@@ -1011,7 +1011,7 @@ uint64_t ShortenInstructions::shortenInstructions(BinaryFunction &Function) {
       if (opts::Verbosity > 2)
         OriginalInst = Inst;
 
-      if (!BC.MIB->shortenInstruction(Inst))
+      if (!BC.MIB->shortenInstruction(Inst, *BC.STI))
         continue;
 
       if (opts::Verbosity > 2) {

bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp

@@ -51,7 +51,9 @@ public:
     return false;
   }
 
-  bool shortenInstruction(MCInst &) const override { return false; }
+  bool shortenInstruction(MCInst &, const MCSubtargetInfo &) const override {
+    return false;
+  }
 
   bool isADRP(const MCInst &Inst) const override {
     return Inst.getOpcode() == AArch64::ADRP;

bolt/lib/Target/X86/CMakeLists.txt

@@ -1,5 +1,6 @@
 set(LLVM_LINK_COMPONENTS
   BOLTCore
+  BOLTUtils
   MC
   Object
   Support

bolt/lib/Target/X86/X86MCPlusBuilder.cpp

@@ -23,6 +23,7 @@
 #include "llvm/MC/MCInstrInfo.h"
 #include "llvm/MC/MCRegister.h"
 #include "llvm/MC/MCRegisterInfo.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/DataExtractor.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/Errc.h"
@@ -35,6 +36,17 @@
 using namespace llvm;
 using namespace bolt;
 
+namespace opts {
+
+extern cl::OptionCategory BoltOptCategory;
+
+static cl::opt<bool> X86StripRedundantAddressSize(
+    "x86-strip-redundant-address-size",
+    cl::desc("Remove redundant Address-Size override prefix"), cl::init(true),
+    cl::ZeroOrMore, cl::cat(BoltOptCategory));
+
+} // namespace opts
+
 namespace {
 
 unsigned getShortBranchOpcode(unsigned Opcode) {
@@ -2031,14 +2043,26 @@ public:
     llvm_unreachable("not implemented");
   }
 
-  bool shortenInstruction(MCInst &Inst) const override {
+  bool shortenInstruction(MCInst &Inst,
+                          const MCSubtargetInfo &STI) const override {
     unsigned OldOpcode = Inst.getOpcode();
     unsigned NewOpcode = OldOpcode;
 
-    // Check and remove EIZ/RIZ. These cases represent ambiguous cases where SIB
-    // byte is present, but no index is used and modrm alone shoud have been
-    // enough. Converting to NoRegister effectively removes the SIB byte.
     int MemOpNo = getMemoryOperandNo(Inst);
+
+    // Check and remove redundant Address-Size override prefix.
+    if (opts::X86StripRedundantAddressSize) {
+      uint64_t TSFlags = Info->get(OldOpcode).TSFlags;
+      unsigned Flags = Inst.getFlags();
+
+      if (!X86_MC::needsAddressSizeOverride(Inst, STI, MemOpNo, TSFlags) &&
+          Flags & X86::IP_HAS_AD_SIZE)
+        Inst.setFlags(Flags ^ X86::IP_HAS_AD_SIZE);
+    }
+
+    // Check and remove EIZ/RIZ. These cases represent ambiguous cases where
+    // SIB byte is present, but no index is used and modrm alone should have
+    // been enough. Converting to NoRegister effectively removes the SIB byte.
     if (MemOpNo >= 0) {
       MCOperand &IndexOp =
           Inst.getOperand(static_cast<unsigned>(MemOpNo) + X86::AddrIndexReg);
@@ -3877,7 +3901,7 @@ public:
         return BlocksVectorTy();
 
       CompareInst.addOperand(MCOperand::createImm(CaseIdx));
-      shortenInstruction(CompareInst);
+      shortenInstruction(CompareInst, *Ctx->getSubtargetInfo());
 
       // jump to next target compare.
       NextTarget =

bolt/test/X86/addr32.s

@@ -0,0 +1,25 @@
+# Check that we don't accidentally strip addr32 prefix
+
+# RUN: llvm-mc -filetype=obj -triple x86_64-unknown-unknown %s -o %t.o
+# RUN: ld.lld %t.o -o %t.exe -nostdlib
+# RUN: llvm-objdump -d %t.exe | FileCheck %s
+# RUN: llvm-bolt %t.exe -o %t.out -lite=0 -x86-strip-redundant-address-size=false
+# RUN: llvm-objdump -d %t.out | FileCheck %s
+# CHECK: 67 e8 {{.*}} addr32 callq {{.*}} <foo>
+# RUN: llvm-bolt %t.exe -o %t.out -lite=0 -x86-strip-redundant-address-size=true
+# remove test name from objdump output, to only search for addr32 in disassembly
+# RUN: llvm-objdump -d %t.out | grep -v addr32.s | FileCheck %s --check-prefix=CHECK-STRIP
+# CHECK-STRIP-NOT: addr32
+
+.globl	_start
+.type	_start, @function
+_start:
+.code64
+  addr32 callq foo
+  ret
+  .size	_start, .-_start
+
+.globl	foo
+.type	foo, @function
+foo:
+  ud2